This invention relates to a synchronization signal and its use in a method of access to a communication interconnect that connects multiple units.
Communication systems often need a precisely timed synchronization pulse or signal, but if there is not a separate path for this purpose, then other signals on the interconnect can interfere with the synchronization signal. In the time period between synchronization signals, it is desirable to guarantee that certain units receive at least one clear opportunity to access the interconnect. For the rest of the time, it is desirable to allow units to attempt access to the interconnect at any time as the demand arises.
In existing interconnects, synchronization signals might be carried on a dedicated channel or connection so there is no interference. However, this requires additional physical media or channel allocation. When carried on the same channel as other signals, the synchronization signal might be encoded to protect it from interference. For example, one known synchronization method requires that the data have a structure that repeats at fixed intervals with an embedded synchronization signal. This does not work well with the unstructured data often found in computer systems. Yet other systems allow the synchronization signal to arrive at irregular intervals that can be averaged over a long period of time to derive a more stable average timing. This requires averaging circuitry or software and may take a long time to generate a stable signal. Known access methods either allow all units to attempt access to the interconnect at any time, without guaranteeing access to any; or they allocate every unit equal access to the interconnect and do not provide the flexibility to provide more accesses to those units having more data to send, while the other units are primarily idle. These and other disadvantages are overcome by the synchronization signal method and apparatus of this invention.
This invention does not require a separate dedicated synchronization channel or path, is readily adaptable to unstructured data, and can provide highly accurate synchronization through self-correction of the timing of the synchronization signal. This synchronization signal also initiates a period of time of sequentially assigned access to the interconnect, before returning to a demand-driven access method.